Can anyone sustain my sick betta?

I don't know if anyone can help me, but I have a betta who is sick. I thought he have Dropsy, because his sides have become very swollen and his scales started to stick up, but he has be this way for I'd estimate three or four months, and I've read that Dropsy usually kills inside 15 days. He is in a small aquarium with filter. He has a predisposition to lean on the side that is most swollen, but he props himself against ornaments to stay straight. He hasn't loss color and is still eating. He eats pellet, not live food or flakes. He mostly lays at the bottom, but will still swim up for air. I clean the tank every 1 to 2 weeks. I also attach salt to the water. When he first started getting sick, as I said, I thought he had Dropsy so I put Maracyn-Two within the water, but that didn't help. I've also tried raising the wet temperature and adding Aquari-Sol to see if that would assist with sluggishness, but nothing is working. I'm not sure what else to do. Any guidance?

By "small aquarium", what do you mean, how small? He should be surrounded by a 3 gallon tank at least. You should be cleaning 25% of his tank every week. Betta's can live to be 5 to 6 years antediluvian when cared for VERY properly, and well. Check your water, are your nitrates/nitrites soaring? Also, is your ammonia high? He could be suffering from some kind of ammonia burns. I suggest you purely test your water, or take a taster of it into a pet store, and they can test it for you. You should be putting one tablespoon of aquarium salt in his container, per every 10 gallons of water. As well, make certain you are not over-feeding him! 2-4 pellets every other day is the maximum that Betta fish can be fed. Their stomachs are almost as big as their eye, you cannot feed them anymore. Make sure you are soaking his pellets beforehand, and later dropping them into his tank, also, make SURE he is not in a bowl - bowls are for food, not pets. He could be suffering from swim bladder disorder, which is cause when fish inhale oxygen into their systems.
you said you put brackish in the water, i hope it isn't table salt and i hope you haven't put too much contained by

does he have filter and heater?

how long have you have him. it might just be old age
Answers:    To be honest with you, from what I have personally observed, 3 is the average age for a betta, although, yes, they can live to be longer. I've just had a few bettas live to be 5 though, and I've had quite a few since I breed them.

Your betta most potential has either swim bladder disorder or some sort of internal parasite, with the former anyone much more likely. Here is some information on SBD I found:

"Initially, fast the fish for 2 - 3 days and then nurture peas, lightly boiled/steamed, de-skinned and mushed (this is a cure for constipation). If this is not effective, increase the tank heat to approx. 78-80F and add Epsom Salts - an eighth of a teaspoon per 5 gallons. If this is not effective, treat with a medicated food or a broad-spectrum antibiotic (suggestions are Medigold or MetroMed or Maracyn 1 and 2 within US, Myxazin in UK). If this is not effective, treat with an internal parasiticidal medication." (credit to http://www.kokosgoldfish.com/Swim%20Blad...

If it turns out to be a parasite, I recommend using Jungle's Parasite Clear for internal fleas and anti-parasitic foods, which has always worked for me. If it's Swim Bladder, I have used anti-bacterial food along near the tips I posted above. If none of this works, feel free to send me an email. I will be glad to help you out.
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